A new study suggests that Americans probably gain about a pound during the winter holiday season  but this extra weight accumulates through the years and may be a major contributor to obesity later in life.

This finding runs contrary to the popular belief that most people gain from five to ten pounds between Thanksgiving and New Year's Day.

This conclusion was reached by researchers at the National Institute of Child Health and Human Development (NICHD) and the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). The results of their study appear in the
March 23 New England Journal of Medicine.

"These findings suggest that developing ways to avoid holiday weight gain may be extremely important for preventing obesity and the diseases associated with it," said NICHD Director Duane Alexander, M.D.

According to government statistics, more than half of all adult Americans are overweight, as defined by body mass index, said Jack A. Yanovski, M.D., Ph.D., the study's principal investigator and head of NICHD's Unit on Growth and Obesity. Body mass index is a mathematical formula used to correct body weight to account for a person's height. According to Dr. Yanovski, the latest national surveys show that 54.9 percent of Americans have a body mass index of 25 or more and are overweight, while 22.3 percent are considered obese, with a body mass index of 30 or more.

"The prevalence of obesity in the U.S. has increased dramatically over the past decade," Dr. Yanovski said. "Weight gain during adulthood may contribute to heart disease, diabetes, and other serious health problems."

"Because losing weight is so difficult, it is important to learn when and why people gain weight so that effective strategies to prevent obesity can be developed, " said study co-author Susan Z. Yanovski, M.D., Executive Director of NIDDK's National Task Force on the Treatment and Prevention of Obesity.

Previous studies suggested that Americans gain an average of 0.4 to 1.8 pounds each year during their adult lives, Dr. Yanovski said. It was unknown, however, if people gained weight at a steady rate throughout the year, or just at certain times, such as during the winter holiday season. To find out just how much of this weight increase occurred over the holidays, Dr. Yanovski and his colleagues measured weight and collected other health information from 195 volunteers. These volunteers worked at, or lived near, the NIH campus in Bethesda, MD. The group was racially, ethnically, and socioeconomically diverse. The study's participants ranged in age from 19 to 82 years, and in weight from 95 to 306 pounds. In all, 51 percent were women, and 49 percent were men. The percentage of volunteeers who were at a healthy weight, were overweight, or were obese was similar to that of the U.S. adult population. All 195 were weighed at six-week intervals before, during, and after the winter holiday season; 165 returned for additional measurements in June and in September, one year after the study began.

Compared to their initial weight in late September or early October, the volunteers gained just over a pound (1.05 lb) by late February or early March. Most of that weight gain (0.8 lb) occurred during the six-week interval between Thanksgiving and New Year's Day. The researchers asked the volunteers about several factors that might influence weight change, such as stress, hunger, activity level, changes in smoking habits, or number of holiday parties they attended. The researchers found that only two factors influence weight gain: level of hunger and level of activity. Volunteers who said they were much more active or much less hungry since their last clinic visit were the least likely to gain weight over the holidays, and some even lost weight. Those who reported being less active or more hungry had the greatest holiday weight gain.

"The finding that study volunteers reporting more physical activity had less holiday weight gain suggests that increasing physical activity may be an effective method for preventing weight gain during this high-risk time," Dr. Yanovski said.

The researchers also found that study volunteers believed that they had gained much more weight than they actually had over the holidays, overestimating their weight gain by slightly more than 3 pounds. Fewer than 10 percent of subjects gained more than 5 pounds over the holiday season. However, Dr. Yanovski added, overweight and obese volunteers were more likely to gain five pounds than were those who were not overweight, which suggests that the holiday season may present special risks for those who are already overweight.

"Although an average holiday weight gain of less than a pound may seem unimportant, that weight was not lost over the remainder of the year," Dr. Yanovski said. When 165 of the study volunteers were weighed a year after the study began, they had not lost the extra weight gained during the holidays, and ended the year a pound and a half heavier (1.4 lb) than they were the year before.

"This is a 'good news/bad news' story," said Dr. Yanovski. "The good news is that people don't gain as much weight as we thought during the holidays. The bad news is that weight gained over the winter holidays isn't lost during the rest of the year."

The knowledge that people actually accumulate a large proportion of their yearly weight gain over the winter holiday season, the researchers added, may prove useful in treating overweight and obesity.

"...the cumulative effects of yearly weight gain during the fall and winter are likely to contribute to the substantial increase in body weight that frequently occurs during adulthood," the researchers wrote. "Promotion of weight stability during the fall and winter months may prove useful as a strategy to prevent age-related weight gain in the United States."

The NICHD and NIDDK are two of the Institutes comprising the National Institutes of Health, the Federal government's premier biomedical research agency. NICHD supports and conducts research on the reproductive, neurobiological, developmental, and behavioral processes that determine and maintain the health of children, adults, families, and populations. The NICHD website,
http://www.nichd.nih.gov,
contains additional information about the Institute and its mission.

The National Institute of Diabetes and Digestive and Kidney Diseases supports and conducts research on many of the most serious diseases affecting public health, such as diabetes and other endocrine disorders, inborn errors of metabolism, digestive diseases, obesity, nutrition, urology and renal disease, and hematology. For additional information, see
http://www.niddk.nih.gov.